Piezoelectric crystal apparatus



May 4, 1937.

J. M. WOLFSKILL PIEZOELECTRIC CRYSTAL APPARATUS Filed Aug. 28, 1936 2 Sheets-Sheet l .5 mm M I ,7 r w. I

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PIEZOELECTRIC CRYSTAL APPARATUS Filed Aug. 28, 1936 2 Sheets-Sheet 2 m H 6 6 2 flu under, Z9 27 h oysk gl l,

Patented May 4, 1937 UNITED STATES PATENT OFFICE 14 Claims.

This invention relates to piezo-electric crystal apparatus and more particularly to a device for varying the frequency of a piezo-electric controlled oscillation generator.

An object is to permit the continuous variations of the frequency of one or more piezoelectric crystals over a definite frequency range.

Another object is to permit the use of several crystals successively and obtain a continuous valo riation of frequency over a wide range.

A further object of this invention is to provide a simple and easily constructed crystal holder in which the frequency may be varied by means of an air-gap adjustment, such that supersonic resonance points between the crystal surface and movable electrode will not affect the free oscillation of the crystal.

Still another object of this invention is to obtain the maximum frequency variation of a crystal by means of the air-gap without materially reducing the output of the crystal controlled oscillation generator.

Still another object of this invention is to provide a holder in which the crystal is, at all times,

rigidly held in position even for maximum airgap adjustment and in which free oscillation of the crystal is not hindered.

Still another object is that one edge of an electrode of the holder is in contact, or substantially in contact, with the crystal at all times,

and facilitates starting of crystal with less feedback over a wider frequency range.

A feature of the invention is a piezo-electric crystal holder arranged for one, two, or any num- 5 ber of crystals with a bottom and top electrode on each crystal; the top electrode of each crystal is movable toward and away from the crystal face, said electrode acting like the cover of a book, in that this electrode may be moved angularly with respect to the crystal face and cause variation of the frequency of the crystal.

Another feature of this invention is the method of varying the air-gap such that supersonic air resonance between the crystal face and the movable electrode is greatly minimized. Such resonance as may occur is only over a very small area of the plate since the air-gap is in the shape of a wedge and at no time is there more than a line area which has the required distance for resonance to occur. For a 3500 kilocycle crystal air resonance would occur at approximately .002 of an inch electrode spacing from the corresponding crystal face, at which point the reflected supersonic wave meets the incident wave and tends to dampen the mechanical oscillations of the crystal. It can easily be seen that in a parallel type air-gap the entire area of the crystal will be affected by this air resonance, and this very markedly, not only where the electrode surface is'displaced .002 of an inch from the crystal surface, but all integral multiples of this distance. The output of such a crystal controlled oscillator drops very materially at all these points or electrode spacings.

Another feature of this invention is that one edge of the electrode is at all times in contact with the crystal, thus facilitating starting of the crystal into oscillations over a wider frequency range.

The crystal is also at all times clamped in position by the spring action on the top electrode.

By using the same type of air-gap any number of crystals may be incorporated in one unit and by a cam arrangement shown in the drawings and described in the specification a continuous variation of frequency over a wide range is possible, with practically constant output over this range, and with no external switching arrangement. All necessary switching from one crystal to the next being taken care of by a suitable arrangement in the cam, each crystal is connected into circuit within the holder at the proper time and maintained connected for the period over which it is undergoing a complete variation of air-gap from minimum to maximum. This corresponds to a frequency variation of the crystals zero air-gap frequency to its maximum air-gap frequency. After this maximum frequency variation is obtained from a crystal, that particular crystal is disconnected and the next adjacent crystal which is ground to a frequency approximately '7 kc. higher for a 3500 kc. crystal, at zero air-gap, is engaged and is in its minimum air-gap position when first connected; as the cam is rotated the frequency of this latter crystal is varied through a '7 kc. range, after which another crystal may be engaged, and so on.

The dial on any one of these units may be calibrated in kilocycles variation and any set ting may be duplicated with a reasonable degree of accuracy.

A more detailed description of the operation of this device is set forth in the following specification and drawings, in which, briefiy,-

Figure 1 is a sectional view of a single crystal unit holder;

Fig. 2 is a sectional view in vertical elevation, showing a single crystal unit holder;

Fig. 3 is a sectional view along the line 33 of Fig. 2;

Fig. 4 is a view of a multiple crystal holder;

Fig. 5 shows the holder of Fig. 4 in vertical sectional elevation, taken along the line 55 of Fig. 6;

Fig. 6 is a view taken along the line 6-6 of Fig. 5;

Fig. 7 is a sectional view taken along the line 1-1 of Fig. 6;

Fig. 8 is a sectional view taken along the line 8-8 of Fig. 5; and

' most position.

Fig. 9 is a bottom plan view of the control dial.

Referring to Figs. 1, 2 and 3 of the single crystal holder, the piezo-electric crystal I is held in position by plates 2 and 3 which serve as the electrodes. Attached to plate 2 is a U-shaped spring 4, the ends of which rest in notches 5, in the side of the cavity of the holder 6, made of some suitable insulating material. Spring 4 constantly holds plate 2 against screw pin 1 to which is fastened dial and knob 8. Screw pin 7 is screwed through the metal top plate 9 and thus causes electrode 2 to move toward and away from the crystal l, varying the air-gap between the crystal i and electrode 2. This causes a frequency variation of the crystal due to the variation of the capacity of the air-gap which is in effect in series with the crystal. The dial 8 may be calibrated in terms of cycles or kilocycles variation and a suitable indicator It! may be attached to the holder 6. Electrical connection is made to the bottom plate 3 through the pin Ii. The movable electrode 2 is connected through screw pin 1' and top plate 9 which is fastened by a screw 9a to a metal insert i2 which is in turn fastened to contact pin i3. Connection can also be made to plate 2 by means of a flexible wire fastened to the pin i3, if desired. The pitch of the thread of screw i can be made such that for one complete rotation of the dial El the plate 2 will be caused to move through its entir mstance.

Where desired several pieZo-electric crystals may be obtained and placed each into a separate holder, such as shown in Figs. 1, 2 and 3. The crystal in each holder is ground to have a frequency different from that of the other crystals; however, the frequency ranges of all of the crystals, taken together, may be such to cover a given band of frequencies from one end to the other continuously. A transmitter employing an arrangement such as this may be operated on any one of the frequencies within this band or frequency channel or channels. This is a material advantage where a large number of stations, particularly frequency controlled stations, are operated in a particular band of frequencies. If one of this large number of stations interferes with another, then the operator of the station interfered with may change its frequency sligh ly to avoid the interference. This frequency change may be accomplished readily with my invention, using one or a limited num er of crystals, and a large variation in frequency selection may be obtained.

The holder of this invention is adapted for use with crystals which vary in size and frequency over a wide range. When used with crystals having a thickness vibration frequency in the range of 3500 kilccycles, a variation of '7 kilocycles is possible, for which the maximum vari ation of the air-gap at the edge of the plate is approximately Referring to Figs. 4 to 9, inclusive, in which the multiple crystal variable frequency holder is illustrated, the two pieZo-electric crystals i5 and i6 rest on a suitable metal plate l? which acts as a common electrode for both crystals. The two movable top electrodes l8 and i9 with their associated U-shaped springs '22 and 2i are similar to plate 2, shown in Figs. 1, 2 and 3. These springs rest in notches 22 provided for in the molded body of the holder 23 which is made of some suitable insulating material, and tend to maintain the electrodes 18 and iii in their upper- Plates l8 and 29 are depressed against the spring pressure by two metal plungers 2d and 24d which make contact with the plates by the action of a cam 25 as the latter is rotated. This cam is made of some suitable insulating material with a metal contact 26 attached thereto. This metal contact is connected to the shaft 2'! and also to a lug 28 which serves to make electrical contact with top movable electrodes. The metal contact 26 carried by the cam 25 serves as a commutator alternately to connect the two top electrodes l8 and I9 to the lug connection as the knob 29 is rotated. Connection 38 serves to connect the other electrode of the crystal to the external circuit. The two plungers 24 are spaced diametrically opposite in the holder and are free to move up and down through holes in the insulating material which serve as bushings.

The shaft receiving hole in the cam 25 is disposed at a slight angle with respect to the perpendicular, so that when fastened to shaft 21 by means of a set screw 32, the surface of the cam will be at an angle to the surface of the holder.

By rotating the cam 25 by means of knob 29 the plungers 24 are caused to reciprocate back and forth alternately, and move the two electrodes 18 and I9 up and down alternately. At the same time, electrical connection is made to the electrodes l8 and i9 alternately through the metal contact 26 in the cam.

The cam is tilted at such an angle that the plunger and electrode which is in contact with the metal member 26 shall move from a minimum to a maximum position while in contact with said metal member 26; after reaching the maximum position this contact is broken between the first plunger and said member 26 and connection is established with the other electrode which is then in its minimum position. This latter electrode then remains in contact with the member 25 while the cam is rotated when its maxi mum position is reached. The direction of rotation of the cam can then be reversed, and the same cycle will be repeated in the opposite direction.

A relatively strong spring 33 is provided on the shaft 2'! to allow for slight variations in dimensions caused by contraction and expansion of the holder materials, so that the crystals will not be broken due to excess pressure when the electrodes are in the minimum position.

The piezo-electric crystal holder shown in Figs. 4 to 9, inclusive, is made to house two crystal elements; however, it is apparent that the holder may be made to accommodate more crystal elements than two and the cam 25 disposed at a suitable angle or developed in such a manner as to adjust the upper electrode associated with each crystal element at the proper time and to the proper extent, during the rotation of the cam, the same as is accomplished in a two crystal element holder. The crystal elements for a frequency of 3500 kc. are ground to predetermined frequencies spaced approximately 7 kilocycles apart, for example, this frequency being determined at minimum electrode spacing. The frequency of each crystal element may be varied over a band of frequencies '7 kilocycles wide by varying the electrode spacing from minimum to maximum, and a wide band of frequencies may be covered, dependupon the number of crystal elements used.

Thus my invention provides an easy and reliable apparatus for changing from one frequency to another gradually, or for varying the frequency of the crystal controlled oscillation generator or crystal filter circuit.

In using my invention in a vacuum tube oscillation generator employing a variable tuned or resonant circuit adjusted to the frequency or harmonic of the crystal element, the variabletuning control may be connected mechanically to the knob 29 or cam 25 to be operable simultane-' ously therewith. Thus the operator may shift frequency by manipulating only one control.

Various modifications in the details of construction may be made in my invention without departing from the spirit and scope of the invention. Therefore, I do not desire to limit this invention to the exact details described and shown in the foregoing specification except insofar as those details may be defined in the claims.

What I claim is as follows:

1. A piezo-electric crystal holder comprising a body of insulation material for housing a crystal element, a pair of electrodes one above'and one below the crystal element, means for moving said electrode above said crystal element angularly with respect to the upper face of said crystal element, said means including a resilient member engaging said upper electrode and said body and exerting pressure tending to increase the angle between said upper electrode and the upper surface of said crystal element, and a rotatable and adjustable member engaging said upper electrode for increasing or decreasing the angle between said crystal element and said upper electrode.

2. A piezo-electric crystal holder comprising a r housing for a crystal element, a pair of electrodes in said housing, said electrodes being disposed one above the other, a resilient member attached to the upper one of said electrodes for moving said upper electrode angularly with respect to the bottom electrode, and a rotatable member for pressing said upper electrode downward against the pressure of said resilient member to vary the angular adjustment between said upper electrode and said bottom electrode to vary the frequency of a crystal element positioned between said pair of electrodes.

3. A piezo-electric crystal holder comprising a housing for a crystal element, a pair of electrodes in said housing, said electrodes being normally disposed one above the other, a substantially U-shaped resilient member having the midportion thereof attached to the upper one of said electrodes and the ends thereof engaging surfaces of said housing for exerting a pressure on said upper electrodes to move said upper electrode angularly with respect to the bottom elec-- trode, and a rotatable member for pressing said upper electrode downward against the pressure of said resilient member to vary the angular adjustment between said upper electrode and said bottom electrode to vary the frequency of a crystal element positioned between said pair of electrodes.

4. A piezo-electric crystal holder comprising a body of insulation material for housing a crystal element, a pair of electrodes one above and one below the crystal element, means for moving said electrode above said crystal element angularly with respect to the upper face of said crystal element, said means including a substantially U- shaped resilient member having the mid portion thereof attached to said upper electrode and the ends thereof engaging said body and exerting pressure tending to increase the angle between said upper electrode and the upper surface of said crystal element, and a rotatable and adjustable member engaging said upper electrode for increasing or decreasing the angle between said crystal element and said upper electrode.

5. Piezo-electric crystal apparatus comprising a piezo-electric crystal element housing having a cavity therein for receiving the crystal element, an electrode on the bottom of said cavity for contacting the lower surface of the crystal element, an electrode in said cavity for contacting the upper surface of the crystal element, and means for adjusting said last-mentioned elec-. trode angularly with respect to the crystal'element and for maintaining the lowermost edge of said last-mentioned electrode in engagement with said crystal element, said means includinga resilient member engaging said last-mentioned electrode and a screw member for pressing said lastmentioned electrode downward against the pres-. sure of said resilient member.

6. Piezo-electric crystal apparatus comprising a piezo-electric crystal element housing having a cavity therein for receiving the crystal element, an electrode on the bottom of said cavity for contacting the lower surface of the crystal element, an electrode in said cavity for contacting the upper surface of the crystal element, and means for adjusting said last-mentioned electrode angularly with respect to the crystal element and for maintaining the lowermost edge of said lastmentioned electrode in engagement with said crystal element, said means including an elon-z gated resilient member attached to said lastmentioned electrode adjacent to an edge thereof in permanent engagement with the crystal element, said resilient member having the ends thereof engaging said housing for exerting an upward pressure on said last-mentioned elec-.

trode, and a screw member for engaging the upper surface of said last-mentioned electrode substantially in the center thereof for pressing this electrode downward or permitting it to rise upward under the action of said resilient member.

7. A piezo-electric crystal holder comprising a housing, a pair of electrodes positioned in said housing for engaging a crystal element therebetween, one of said electrodes being angularly movable with respect to the corresponding crystal element surface, and means for moving said lastmentioned electrode, said means including resilient means engaging both said electrode and said housing tending to raise said electrode with respect to said crystal element and means for counteracting said resilient means and for pressing said electrode downward gradually against the action of said resilient means.

8. A piezo-electric crystal holder comprising a housing, a pair of electrodes positioned in said housing for engaging a crystal element therebetween, one of said electrodes being angularly movable with respect to the corresponding crystal element surface, and means for moving said last-mentioned electrode, said means including means for pressing said electrode downward and means acting against said last means and at least partially surrounding said last means for holding said electrode in engagement with said last means.

9. An adjustable frequency piezo-electric crystal apparatus comprising a plurality of piezo-electrio crystals, electrodes for said piezo-electric crystals, the top electrode of each of said piezoelectric crystals being movable with respect to the top surface of the corresponding piezo-electric crystal, and means for moving the top electrodes of said crystals in a predetermined order to vary the frequencies of said crystals over a predetermined range without interrupting the circuit to the piezo-electric crystal apparatus.

10. An adjustable frequency piezo-electric crystal apparatus comprising a plurality of piezoelectric crystals ground to progressively increasing frequencies, means for varying the frequency of one of said crystals within narrow limits and up to the frequency of the next pieZo-electric crystal, means for connecting said last-mentioned crystal into a work circuit when its frequency is reached, and means for varying the frequency of said last-mentioned piezo-electric crystal within narrow limits.

11. An adjustable frequency piezo-electric crystal apparatus comprising a housing, a plurality of piezo-electric crystals ground to progressively increasing frequencies positioned in said housing, and means comprising a movable elctrode positioned over each of said piezo-electric crystals, cam means for raising or lowering said movable electrodes successively in a predetermined order for varying the frequencies of said crystals successively and continuously between predetermined narrow limits such that the higher frequency limit of one of said crystals substantially coincides with the lower frequency limit of the next one of said crystals, and means for connecting each of the crystals into a work circuit while the frequency of said last-mentioned crystal is being varied.

12. An adjustable frequency pieZo-electric crystal apparatus comprising a housing, a plurality of piezo-electric crystals ground to slightly different frequencies positioned in said housing, a metallic plate forming the bottom of said housing and contacting each of said pieZo-electric crystals, an angularly adjustable electrode for each of said piezo-electric crystals cooperating with the upper face of each of said crystals, and a rotatable cam journaled in said housing for varying the angular adjustment of said adjustable electrodes to vary the frequencies of said crystals, in a definite predetermined manner or order.

13. An adjustable frequency piezo-electric crystal apparatus comprising a housing, a plurality of piezo-electric crystals ground to slightly different frequencies positioned in said housing, a metallic plate forming the bottom of said housing and contacting each of said piezo-electric crystals, an angularly adjustable electrode for each of said piezo-electric crystals cooperating with the upper face of each of said crystals, a rotatable cam journaled in said housing for varying the angular adjustment of said adjustable electrodes to vary the frequencies of said crystals, and a contact member attached to said cam for contacting said adjustable electrodes in a predetermined order as said cam is rotated for connecting a selected crystal to an electric circuit.

14. An adjustable frequency piezo-electric crystal apparatus comprising a housing, a plurality of piezo-electric crystals ground to slightly different frequencies positioned in said housing, a metallic plate forming the bottom of said housing and contacting each of said piezo-electric crystals, an angularly adjustable electrode for each of said piezo-electric crystals cooperating with the upper face of each of said crystals, a resilient,

member attached to the top of each of said adjustable electrodes and engaging said housing, a 

